Volcano - created from Mind Map_1

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General

Magma vs Lava

Types of rocks

TYpes of magma

Factors affecting viscosity

Basaltic eruptions

Andestic eruptions

Extrusive

Intrusive

Basalt

Andesite

Rhyolite

Gabbro

Granite

Diorite

Basaltic

ANdestic

Divergent

Convergent

Temperature

Dissolved Gases

Amt of Silica

Materials

Pyroclastic material

Eruption clouds

Eruption coloums

Gases

Lava

Tephra

Pyroclastic flow

Distribution

Subduction zones

Sea floor spreading centers

Hot Spots

OC-OC

OC-CC

Mt PInatubo

Mt St Helens

OC

CC

Mid Atlantic Ridge

East African Rift

Hawaii

Yellowstone National PArk

Effects

Primary

Secondary

Lava Flows

Pyroclastic Flow and surges

Ash & Tephra fall

Volcanic Gases

Iceland (1783)

Mt Debbie (1902)

St Helens

Lake Nyos Crater

Lahars

Ground Deformation

Volcanic Landslides

Tsunami

Flooding

Climate changes

Famine and Disease

Galunggung Indo (1983)

St Helens

St helens

Indonesia 1883

Iceland

Mt Pinatubo

Mt PInatubo

Prediction

Volcanic monitoring

Seismic studies

Ground Deformation

Changes in temp in springs and lakes

Changes in output of surface

Changes in gas composition

Local Seismic Activity

Disadvantage

Sakurajima, Japan

Taal, Phlipi (1965)

Japan, 1989

New Zealand, 1968

Mt Pinatubo and Mt St Helens

Mitigation

Environmental Control

Comm Preparedness

Land Use planning

Bombing

Water sprays

BArriers

LImitations

Mt Etna 1983

Iceland 1973

Hawaii 1960

Indonesia

DC

LDC

Vesuvius Italy

Mt Pinatubo

Galanggung

Hawaii

Management

Technical

Financial

Is a conical or dome shaped landform built by the emission of lava and its contained gases from a constricted vent on the earth's surface

Begins when a fissure develops in the crust and magma forcefully move tpwards the surface through a vent

The form (shape and size) is determined by the composition of magma.

Magma is completely or partly molten material orginatinting from earth's interior.

When it reaches the surface-> Lava

Lava is produced from magma and has generally lost materials that escape as gas

A fragment of rock during a volcanic eruption is known as Pyroclast.

These ejected rocks vary from very fine dust to sand sized volcanic ash.

Typically dark, tempestous omni-loking masses. At a height at which the denisty of material in coloumn is equal to the atm, coloumn will spread out laterally to form mushroom shaped clouds.

As the magma approaches the surface, rapid decompression causes the gases to expand and produce violent upward thrust of a dense mixture of hot gas and tephra.

This is mixture rises rapidly in the cooler air above the vent to form the coloumn and may reach as high as 45km.

Magma contains varying amount of disolved gases held in molten rock by confining pressure

They make up 1-6% of the weight of magma and they contribute significantly to the gases that make up the earth's atmosphere

Hot blasts of high pressure gases from beneath that expands the cracks and develop passageway.

2 types: Basalt (major) and Andesite.

Depending on the type of lava flow, the speed and temperarure of the lava differs

80% of world's distribution

5%

Natural hazards result from natural processes within the environment. Difer from environmental disasters (acid rain), whic are cuased by human activity and mismanagement of environment.

Natural hazards have the porential to affect people and the environment. The impact of a hazard may be felt over a wide area; effects may be long term and can be costly to property and dangerous to people.

Volcanic hazards provudes both opportunities and risk for people.

Opportunites: fertile soil, attractive scenery and geothermal power

However volcanoes continue to represnt a serious threat to all property and lives

Volcanic eruptions are not rare events. Some 600 volcanoes that have erupted within history are known as active. Those who havenot in recorded history are knwon an Extinct and in between in dormant

A prediction offers a fairly specific date for an unexpected event whereas forecast is just a statement of likelihood

To spredict, one needs to study the volcano's behavior

-Historic styles of eruption (type of activity and affected area)

-When the eruption will take place based on its eruption interval

No means of preventing volcanic eruption but attempts have been made to control lava flows

Solidify at the earth surface

crystalling at depth

Higher the temp, lesser viscous, flow more easily

more gases, more buoyant and fuid. so higher the temperature, more gases present and hence less viscous

more silica, more vscous as it has close jointing and makes it flow slow and difficult for gas to escape.

Low viscosity magma with low dissolved gases amd low silica content but at higher temperature.

Effusive eruption (without explosion) as magma is more fluid and is quiet

Results from the partial melting of the ocean crust at the subduction zone at convergent boundaries

More viscous, flows slowly and travels less distance

Intermediate rock (andesite)

High silica content ]

Explosive eruption due to the presence of more viscours and high gas content.

More gas can dissolve As the gas bubble rises, less pressure and the bubbles expand and hence explode

Fine materials transported by high atm winds. Debirs eventually settles back onto the earth surface by gravity

Mixture of gas and pyroclastic debris that is so dense that it hugs the ground as it flows rapidly into low areas. Can travel up to 100km fromt he source at speeds of 700km/hr

Pose more threat to property than human life. The destroy everything in its path and are likely to result in high but localised economic losses, such as agricultural land, buildings and roads

The most dangerous are the eruptions of basaltic magma which reachs speeds of 50km/hr on steep slopes. Andestic and rhylolitic and more viscous and hence only travel upto 8k from its source.

Mixtures of hot fragments or rocks, lava [articles and ash with hot gases. Related to subduction zone volcanoes.

Flows can travel up to 90km from the source at high speeds. As the material is denser than surrounding air, moves close to the ground to low areas

The force and volume of the material is projected down the volcano rather than into the atm. And due to high temp and speed, destroy everything in its path.

Ash (diamerter of 2mm) forms when magma is fragmented by explosion. The finest ash is carried away by wind into the atm and even into the strata.

Ash fall is more of a nuisance than a cause of death; people exp breathing difficulties and large accumulation ma cause buildings to collapse

Active volcanoes produce large amounts of SO2, C02, H20, Cl2. CO2 is most dangerous as they are denser than air and may cause suffocation

Mudflows of volcanic materials and they represent the 2nd greatest threat to people

hughe amounts of sh and debris produced by eruptions can mix with water and them move rapidly long distamces (less viscous)

occurs widelyas volcanoes grow from within by magma intrusion and as new layers of lava and pyroclasoc material accumulate on the surrounding slopes

Deformation may trigger mass movement hazards.

gravity driven slides of masses of rock and loose volcanic material.

Ground deformation may also trigger mass movement due to instability of slope

Giant waves formed due to huge undersea EQs

Common following volcabnic eruptions as rivers are blocked by lahar or lava flows.

Climate effects result primarily from volcanic ash that is ejected into the strata

the ejection can cause reduction in global av temp and is believed to be an agent of past climate change

Blocks incoming solar radiation

Damage to agricultural land and livestock.

left 35000 homeless and buried 94000ha of cropland

Debris avalanche advanced 20km

30m high waves and drowned 36000 people.

Volcanoes buried under permanent ice caps caused the emlting pf ice and hence a glacial burst (huge gush of water)

In 1991, blasten more that 8km3 of ash and caused global cooling for 2 years and caused the temp to fall by 1degree celcius

Most of the deaths were caused by disease, lack of water and sanitation.

Greatest lava related disaster in history when lava flowed out a 24km long fissure for more than 5 months.

Killed all but 2 out of the 29000 inhabitants

Deopisition of 30kg/m3 on agricultural cropland and hence caused a reduction in agricultural activity.

The burst of gas reahed over 100m above livestock and took 1700 lives and 8000 livestock

Facilitates prediction and monitoring in 2 ways

1. allows scientist to track distribution and movement of magma

2. Makes possible the detection of anomalies- onset or progression of volcanic activity

Seismic waves are released during EQs and expolsions.Certain Waves (S-waves) cannot travel liquids and scientists exploit this fact to study the distribution of magma.

Using controlled explosives, generating seismic waves and a seismograph an the other side of the volcano. If a body of liquid lies in the path of the waves, the wave is blocked and forms a so called shadow. through this scienctists can study the movement of magma.

Electromagnetic seisometersconvert the shaking of the earth into varying electical voltage. this tells us 2 things: amt of energy released, and the source of the eruption (indication where the next eruption might take place.

Maps of EQ epicentre can show the movement of magma

Giant eruptions are preceded by a change in the hsape of the ground or elevation due to the swelling of underlying magam. this can be detected by tilt meters

GPS, to determine latitude, longitude and elevation and has been successfully employed to predict ground formation.

In some cases, temp of lakes near a volcano rises prior to an eruption. In other cases, temp rises and fals again prior to an eruption.

Water levels also may change as evaporation rates increases and hence water levels reduces

Ground temp may also face changes near volcanoe. Thermal sensoring deveices have been placed near these volcanoes to notice the subtle changes

Composition of gases have been noticed to change prior to an eruption. Amts of HCL and SO2 have been noticed to increase in proportion to H20

Several types of seismic activty have been related to eruptions

Local small EQs and tremors

Accurate prediction is particularly difficult with volcanoes reawakening after a long dormancy

Volcano is Montserrat had many false alarms

Preparedness will save many times. Evacuation can save lives but adv prep, management structures to org food, temp housing are needed.

Land zoning and the selection of safe sites depends on estimating probability of volcanic activity. Past eruptions require geological dating tech.

Major limitation is the lack of knowledge of the size of future eruption and extent of the surges. Also the environmental conditions durin geruption (snow cover)

Due to these problems, zoning maps are restricted to certain areas.

Aerial bombing of fluid lava may cause flow to spread and halt the advancing lava, depriving it from its suppkys

Used to control lava flows. Only possible in areas where volcano is surrounded by large bodies of water

Buit to protect against secondary hazards of lahars from property

30% of lava was diverted from its source

artificial moulds to enabke villagers to escape to higher grounds

Physical protection depends on the construction of sediment trap. But these stuctures are expensive and have a limited life span. Located only where lahars path are well defined and not for major destructive flows

Building and structure design can do resist lava and lahars. Volcanic ash on roof esp if its wet, can cause it to collapse. hence roofs must be strong and steep sided.

has 9 hazard zones ranked on the probability of land coverage by flows.

tends to be more successful owing to the fact for better finanical and technical support.

Volcanic Diastser Assistance programme is needed as the past 15 yrs, volcanoes have taken away 29000 lives and forced 800000 out of their hi=omes and cost $3bill cost to damage

emergency planning was not well developed due to unwillingess for local authorities to accept wither the risk of disaster or cost of the damage

Lenght of time available for an alert differs. For densely pop areas, necessary for evacuation to take place as much earlier as possible.

Increasing efforts to encourage local populations to preapre for volcanic disastersb

3X the number of evacuees than any other eruption

75000 successfully evacuated

Usually supplied by DCs as it involves the use of high cost equipment and expertise to try to forecast events

IS used as startegy before and after an eruption and aid tobe effective management, a givernment must be willing to recieve aid from other nations

Volcano

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